From ec55b3758fc7ac82f5a16105dd8cdf8c6bcb2ed5 Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Fri, 10 Aug 2018 23:51:04 +0200
Subject: [PATCH] Add RDF.DateTime.tz/1

---
 lib/rdf/datatypes/date_time.ex         | 16 +++++++++
 test/unit/datatypes/date_time_test.exs | 45 ++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/lib/rdf/datatypes/date_time.ex b/lib/rdf/datatypes/date_time.ex
index 8ce94059..8adcb342 100644
--- a/lib/rdf/datatypes/date_time.ex
+++ b/lib/rdf/datatypes/date_time.ex
@@ -54,4 +54,20 @@ defmodule RDF.DateTime do
     NaiveDateTime.to_iso8601(value)
   end
 
+  def tz(datetime_literal) do
+    if valid?(datetime_literal) do
+      lexical = lexical(datetime_literal)
+      case Regex.run(~r/([+-])(\d\d:\d\d)/, lexical) do
+        [_, sign, zone] ->
+          sign <> zone
+        _ ->
+          if String.ends_with?(lexical, "Z") do
+            "Z"
+          else
+            ""
+          end
+      end
+    end
+  end
+
 end
diff --git a/test/unit/datatypes/date_time_test.exs b/test/unit/datatypes/date_time_test.exs
index 56dd3040..47d8b98f 100644
--- a/test/unit/datatypes/date_time_test.exs
+++ b/test/unit/datatypes/date_time_test.exs
@@ -61,4 +61,49 @@ defmodule RDF.DateTimeTest do
     end
   end
 
+  describe "tz/1" do
+    test "with timezone" do
+      [
+        {"2010-01-01T00:00:00-23:00", "-23:00"},
+        {"2010-01-01T00:00:00+23:00", "+23:00"},
+        {"2010-01-01T00:00:00+00:00", "+00:00"},
+      ]
+      |> Enum.each(fn {dt, tz} ->
+           assert dt |> DateTime.new() |> DateTime.tz() == tz
+         end)
+
+    end
+
+    test "without any specific timezone" do
+      [
+        "2010-01-01T00:00:00Z",
+        "2010-01-01T00:00:00.0000Z",
+      ]
+      |> Enum.each(fn dt ->
+           assert dt |> DateTime.new() |> DateTime.tz() == "Z"
+         end)
+    end
+
+    test "without any timezone" do
+      [
+        "2010-01-01T00:00:00",
+        "2010-01-01T00:00:00.0000",
+      ]
+      |> Enum.each(fn dt ->
+           assert dt |> DateTime.new() |> DateTime.tz() == ""
+         end)
+    end
+
+    test "with invalid timezone literals" do
+      [
+        DateTime.new("2010-01-01T00:0"),
+        "2010-01-01T00:00:00.0000",
+      ]
+      |> Enum.each(fn dt ->
+           assert DateTime.tz(dt) == nil
+         end)
+
+    end
+  end
+
 end